Printing with full printer color gamut, through use of gamut superposition in a common perceptual space

Abstract

A technique of merging or "matching" hue pages of a CRT and printer is used to map CRT control signals through a common perceptual space into printer control signals. The system (1) receives a color specification expressed as CRT control signals, (2) locates the specified color within the CRT perceptual gamut, (3) normalizes the two gamuts in perceptual space, (4) determines the relative position of the same color in the normalized CRT gamut, (5) declares that position to be the relative position of that color in the normalized printer gamut as well, (6) unfolds the normalization to determine the absolute position of the color in the actual printer gamut, (7) expresses that position in terms of printer-control signals, and then (8) applies those signals to the printer, to print the specified color. As a result that color, and color changes, specified in terms of CRT control signals are tracked in terms of both printer control signals and actual printer performance. The two device gamuts are in effect mapped to each other; the full gamuts of both are in effect merged. This new mapping preserves relative positions in color space--and thus the capability of the printer to reproduce distinctions between colors seen on the CRT that appear very closely similar. Such discrimination between colors very adjacent in color space is supported nearly throughout gamuts of both devices, even very near the lightness extrema and maximum-saturation point on a hue page. To facilitate processing, the normalized characterizations for the CRT and printer gamuts (taken as triangular) are approximated for each of 360 hue pages by single-point data representing lightness and chroma at the saturation point--or normalized lightness at that point--plus two common lightness extrema for the gamut solid.

We claim: 
     
       1. A method for printing, with a color printer that has an at least partly known color gamut, a color image portion based on initial color specifications for use in a display device that has an at least partly known color gamut; said method comprising the steps of: performing on such initial specifications a transformation that includes the effect of performing these sub-steps: interpreting relative-position values of lightness and chroma, within a display-device hue page that is part of the display-device gamut in a perceptual space, as also being relative-position values of lightness and chroma of a corresponding hue page of the printer gamut in said same perceptual space, and   using said relative-position values of lightness and chroma of the printer gamut, to derive printer signals; and     then applying the printer signals, to control printing of the particular image portion by the printer.   
     
     
       2. A method for printing, with a color printer that has an at least partly known color gamut, a color image composed of plural image portions and based on initial color specifications for use in a display device that has an at least partly known color gamut; said method comprising the steps of: receiving or developing, for a selected particular portion of the image, the initial color specifications expressed in terms of a hue page that is part of the display-device gamut, in a color space related to operation of the display device;   performing on selected ones of said specifications, corresponding to the selected particular image portion, a transformation that has the effect of performing these substeps: based on said selected specifications in terms of the display-device hue page and display-device color space, determining corresponding values of hue, lightness and chroma expressed in terms of absolute position within a display-device hue page in a perceptual color space,   finding hue-page characterizations for the display-device and printer hue pages, expressed in the same said perceptual space, for said determined hue expressed in the perceptual space,   using said found characterization of the display-device hue page, and also using said found absolute-position values of lightness and chroma in the display-device hue page expressed in said perceptual space, to find corresponding first intermediate values of lightness and chroma expressed in terms of relative position within the display-device hue page and in said perceptual space,   employing said found characterization of the printer hue page, and also employing said first intermediate relative-position values of lightness and chroma, interpreted as also being relative-position values of lightness and chroma in said perceptual space within the printer hue page that is part of the printer gamut, to find second intermediate values of lightness and chroma expressed in terms of absolute position in said perceptual space within the printer hue page,   based upon the hue and the second intermediate relative-position values, all expressed in said perceptual space, obtaining new color specifications expressed in terms of the printer hue page and a color space used for operation of the printer, for the particular image portion; and     then applying the new color specifications, expressed in terms of the printer hue page and said printer space, to control printing of the particular image portion by the printer.   
     
     
       3. The method of claim 2, wherein: the specification-receiving or -developing step comprises receiving or developing, for the particular image portion, said initial specifications in the form of signals for respectively controlling red, green and blue intensities.   
     
     
       4. The method of claim 2, wherein: the obtaining substep comprises defining said new specifications in the form of printer signals for respectively controlling cyan, magenta, yellow and black colorant amounts, for the particular image portion; and   the applying step comprises applying the printer signals to control printing of the particular image portion by the printer.   
     
     
       5. The method of claim 2, wherein: the obtaining substep comprises defining said new specifications in the form of printer signals for respectively controlling red, green and blue intensities, for the particular image portion; and   the applying step comprises, within the printer: applying the printer signals to develop further signals for controlling cyan, magenta, yellow and black colorant amounts, for the particular image portion, and   applying the further signals to control printing of the particular image portion by the printer.     
     
     
       6. The method of claim 2, wherein: the specification-receiving or -developing step comprises receiving or developing said initial specifications in the form of signals for respectively controlling red, green and blue intensities;   the obtaining substep comprises defining said new specifications in the form of printer signals for respectively controlling cyan, magenta, yellow and black colorant amounts; and   the applying step comprises applying the printer signals to control printing of the particular image portion by the printer.   
     
     
       7. The method of claim 2, wherein: the specification-receiving or -developing step comprises receiving or developing said initial specifications in the form of signals for respectively controlling red, green and blue intensities;   the obtaining substep comprises defining said new specifications in the form of printer signals for respectively controlling red, green and blue intensities; and   the applying step comprises, within the printer: applying the printer signals to develop further signals for controlling cyan, magenta, yellow and black colorant amounts, for the particular image portion, and   applying the further signals to control printing of the particular image portion by the printer.     
     
     
       8. The method of claim 2, wherein: the first-values-employing substep comprises adjusting said relative-position value of lightness in proportion to the difference between lightness values at the respective maximum-vividness points of the printer and display-device hue pages, respectively.   
     
     
       9. The method of claim 8, wherein: the first-values-employing substep further comprises offsetting said relative-position value of lightness based on at least one difference between lightness values at lightness-extremum points of the printer and display-device hue pages, respectively.   
     
     
       10. The method of claim 2, wherein: the transformation-performing step achieves said effect without directly using raw characterizing data for hue expressed in terms of either the display-device or printer hue page.   
     
     
       11. The method of claim 2, wherein: the transformation-performing step comprises referring to at least one lookup table to find: for the determined hue, the extrema of lightness- and vividness-related parameters on the display-device hue page, and   for that same hue, the extrema of lightness- and vividness-related parameters on the printer hue page.     
     
     
       12. The method of claim 11, wherein: the transformation-performing step further comprises referring to a lookup table to find the printer hue page corresponding to the determined hue.   
     
     
       13. The method of claim 11, wherein: the transformation-performing step proceeds by referring to at least one lookup table to find: the coordinates of the initial specifications expressed in terms of a normalized display-device hue page, and   normalization-reversed corresponding coordinates expressed in terms of the actual printer hue page.     
     
     
       14. The method of claim 2, wherein: the hue-page characterization-finding step comprises finding approximations to the respective shapes of the display-device and printer hue pages.   
     
     
       15. The method of claim 14, wherein: the approximation-finding step comprises finding vertex coordinates for straight-line-bounded figures representing respective simplified shapes of the display-device and printer hue pages.   
     
     
       16. The method of claim 15, wherein: the straight-line-bounded figures are triangles. 
     
     
       17. The method of claim 16, wherein, for the determined hue, the vertex coordinates represent respectively: the maximum-saturation point;   the maximum-lightness point; and;   the minimum-lightness point.   
     
     
       18. A set of lookup tables for use in printing, with a color printer that has an at least partly known color hue page that is part of the printer gamut, a color image based on input color specifications for use in a display device that has an at least partly known color hue page that is part of the display-device gamut: said set of lookup tables being prepared so that the tabulated values correspond to performing steps comprising: interpreting relative-position values of lightness and chroma, within a display-device hue page that is part of the display-device gamut in a perceptual space, as also being relative-position values of lightness and chroma within a corresponding printer hue page in said perceptual space;   employing said relative-position values within the printer hue page to derive printer signals; and   then applying the printer signals to control printing by the printer.     
     
     
       19. The set of lookup tables of claim 18, wherein: the tabulated values correspond to performing additional steps comprising: determining values of hue, lightness and chroma, expressed in terms of absolute position within the display-device hue page in a perceptual color space, that correspond to the input specifications,   finding display-device- and printer-hue-page characterizations, expressed in said perceptual space, for said hue expressed in perceptual space, and   using said found display-device- and printer-hue-page characterizations, and also using the found absolute-position values of lightness and chroma expressed in said perceptual space, to find corresponding first intermediate values of lightness and chroma, expressed in terms of relative position in said perceptual space within the display-device hue page;   wherein said printer-hue-page relative-position-value employing step comprises: using said relative-position values of lightness and chroma within the printer hue page in said perceptual space, produced by said interpreting step, to find second intermediate values of lightness and chroma expressed in terms of absolute position in said perceptual space within the printer hue page, and   based upon the hue and the second intermediate relative-position values, all expressed in said perceptual space, obtaining new color specifications expressed in terms of the printer hue page and a color space used for operation of the printer; and     wherein said new color specifications comprise said printer signals.   
     
     
       20. A method for printing, with a color printer that has an at least partly known color hue page that is part of the printer gamut, a color image composed of plural image portions and based on color specifications for use in a display device that has an at least partly known color hue page that is part of the display-device gamut; said method comprising the steps of: receiving or developing, for a particular image portion, display-device signals for controlling red, green and blue intensities for each image portion, in operation of the display device;   performing on said display-device signals a transformation that has the effect of performing these substeps: determining values of hue, lightness and chroma, expressed in terms of absolute position within a display-device hue page that is part of the display-device gamut in a perceptual color space, that correspond to the signals,   finding display-device- and printer-hue-page characterizations, expressed in said perceptual space, for said hue expressed in perceptual space,   using said found display-device-hue-page characterization to find first intermediate values of lightness and chroma, expressed in terms of relative position in said perceptual space within the display-device hue page, that correspond to the found absolute-position values of lightness and chroma expressed in said perceptual space,   employing the printer-hue-page characterization, and also the first intermediate relative-position values of lightness and chroma, interpreted as also being relative-position values of lightness and chroma in said perceptual space within a corresponding printer hue page that is part of the printer gamut, to find second intermediate values of lightness and chroma expressed in terms of absolute position in said perceptual space within the printer hue page,   based upon the hue and the second intermediate absolute-position values, all expressed in said perceptual space, obtaining printer signals for controlling quantities of cyan, magenta, yellow and black colorants for each image portion, in operation of the printer; and     then applying the printer signals to control printing of the particular image portion by the printer.   
     
     
       21. The method of claim 20, wherein: the obtaining step comprises, outside the printer, defining printer signals for controlling red, green and blue intensities; and   the applying step comprises, within the printer: processing the printer signals to develop further signals for controlling quantities of cyan, magenta, yellow and black colorants, and   applying the further signals to control printing of the particular image portion by the printer.